nebula/noiseutil/nist.go

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package noiseutil
import (
"crypto/ecdh"
"crypto/rand"
"fmt"
"io"
"github.com/flynn/noise"
)
// DHP256 is the NIST P-256 ECDH function
var DHP256 noise.DHFunc = newNISTCurve("P256", ecdh.P256(), 32)
type nistCurve struct {
name string
curve ecdh.Curve
dhLen int
pubLen int
}
func newNISTCurve(name string, curve ecdh.Curve, byteLen int) nistCurve {
return nistCurve{
name: name,
curve: curve,
dhLen: byteLen,
// Standard uncompressed format, type (1 byte) plus both coordinates
pubLen: 1 + 2*byteLen,
}
}
func (c nistCurve) GenerateKeypair(rng io.Reader) (noise.DHKey, error) {
if rng == nil {
rng = rand.Reader
}
privkey, err := c.curve.GenerateKey(rng)
if err != nil {
return noise.DHKey{}, err
}
pubkey := privkey.PublicKey()
return noise.DHKey{Private: privkey.Bytes(), Public: pubkey.Bytes()}, nil
}
func (c nistCurve) DH(privkey, pubkey []byte) ([]byte, error) {
ecdhPubKey, err := c.curve.NewPublicKey(pubkey)
if err != nil {
return nil, fmt.Errorf("unable to unmarshal pubkey: %w", err)
}
ecdhPrivKey, err := c.curve.NewPrivateKey(privkey)
if err != nil {
return nil, fmt.Errorf("unable to unmarshal pubkey: %w", err)
}
return ecdhPrivKey.ECDH(ecdhPubKey)
}
func (c nistCurve) DHLen() int {
// NOTE: Noise Protocol specifies "DHLen" to represent two things:
// - The size of the public key
// - The return size of the DH() function
// But for standard NIST ECDH, the sizes of these are different.
// Luckily, the flynn/noise library actually only uses this DHLen()
// value to represent the public key size, so that is what we are
// returning here. The length of the DH() return bytes are unaffected by
// this value here.
return c.pubLen
}
func (c nistCurve) DHName() string { return c.name }